Spiritual disciplines and the threat of "works righteousness"

In his book on Spiritual Theology, Diogenes Allen considers whehter spiritual disciplines aimed at growing in love of God and neighbor are a form of “works righteousness,” a concern that Protestants often have:

Many Christians are uneasy with the idea that we are to make an effort to overcome our inadequacies because it sounds like “works righteousness,” as if our salvation depended on something we do rather than wholly on God’s grace. But we must remember that God is as fully active and present in our lives when we are making an effort as when we are not. I both instances we rely wholly on God for our existence and powers. It also helps to remember the distinction between justification and sanctification. As the great Protestant reformer John Calvin put it, justification and sanctification are twins. They are both the work of Christ, but each is a distinct work. Justification is our forgiveness or pardon by God apart from the law because of Christ’s death on the cross; sanctification is the process by which we actually begin to become holy, free of the effects of evil and full of charity or divine love. Justification is the beginning of sanctification. Both require divine grace. Divine grace does not mean that there is nothing left for us to do. Quite the contrary, it is precisely because of divine grace that we are able to begin to seek freedom from the effects of sin and evil, and to begin to love in the way Christ loves. (p. 9)

Even Luther, arch-foe of works-righteousness that he was, could write of the necessity of discipline for the Christian life. From The Freedom of a Christian:

Although, as I have said, inwardly, and according to the spirit, a man is amply enough justified by faith having all that he requires to have, except that this very faith and abundance ought to increase from day to day even till the future life, still he remains in this mortal life upon earth, in which it is necessary that he should rule his own body and have intercourse with men. Here then works begin; here he must not take his ease; he must give heed to exercise his body by fastings, watchings, labour, and other regular discipline, so that it may be subdued to the spirit, and obey and conform itself to the inner man and faith, and not rebel against them nor hinder them, as is its nature to do if it is kept under. For the inner man, being conformed to God and created after the image of God through faith, rejoices and delights itself in Christ, in whom such blessing have been conferred on it, and hence has only this task before it: to serve God with joy and for nought in free love.

I think the key distinction here is that, according to the Reformers, we are justified (forgiven, pardoned, etc.) solely on account of Christ and there’s nothing we do to merit salvation in any respect. What they objected to was any suggestion that God accepts us based on some intrinsic quality we posses, even if it is supposed to be wrought by grace (what Robert Jenson called the “anti-Pelagian codicil”).

But, as a consequence of our justification we receive the Holy Spirit who works within us to transform us into the image of the Son of God. But it’s not in virtue of that “actualized” holiness that God accepts us, but only on account of Christ. You might say that sanctification is the working out or making visible of our salvation as we are conformed to Christ’s image, but it’s not the cause of it.